The photocatalytic efficiency of several TiO2 (namely Degussa P25 and Millennium PC50, PC100, PC105, PC500) used as suspensions are compared for the photocatalytic degradation of 3-nitrobenzenesulfonic acid (3-NBSA) and 2,5-anilinedisulfonic acid (2,5-ADSA). With 3-NBSA, P25 is clearly the most efficient and there is no apparent relationship between photocatalytic activity and specific surface area. This result is consistent with that obtained with phenol, but a contrast was noticed with 2,5-ADSA where PC500 is more efficient than P25 in spite of a higher adsorption of the latter. In the case of TiO2 Millennium relative photonic efficiencies zeta(r) are smaller with 3-NBSA than with 2,5-ADSA, that is consistent with the electron-withdrawing effect of nitro group. For the same reason the direct phototransformation in sunlight is much more rapid with of 2,5-ADSA than for 3-NBSA and 4-nitrotoluene-2-sulfonic acid.